Critical assessment of wet-chemical oxidation synthesis of silicon quantum dots

The wet-chemical Si QD synthesis by oxidation of magnesium silicide (Mg₂Si) with bromine (Br₂) was revisited.

Facile synthesis of highly luminescent lithium silicate nanocrystals with varying crystal structures and morphology

The colloidal synthesis of lithium silicate nanocrystals with varying morphology, composition, crystal structures, and high intensity visible luminescence is reported.

Room temperature synthesis of surface-functionalised boron nanoparticles

Capped boron nanoparticles have been synthesized at room temperature by a simple route that does not involve the use of flammable boranes.

Theory of Alkyl-Terminated Silicon Quantum Dots

We have carried out a series of ab initio calculations to investigate changes in the optical properties of Si quantum dots as a function of surface passivation. In particular, we have compared hydrogen-passivated dots with those having alkyl groups at the surface. We find that, while on clusters with reconstructed surfaces complete alkyl passivation is possible, steric repulsion prevents full passivation of Si dots with unreconstructed surfaces. In addition, our calculations show that steric repulsion may have a dominant effect in determining the surface structure and eventually the stability of alkyl-passivated clusters, with results dependent on the length of the carbon chain. Alkyl passivation weakly affects optical gaps of silicon quantum dots, while it substantially decreases ionization potentials and electron affinities and affects their excited state properties. On the basis of our results, we propose that alkyl-terminated quantum dots may be size selected, taking advantage of the change in ionization potential as a function of the cluster size.

Optical Properties of Silicon Clusters in the Presence of Water: A First Principles Theoretical Analysis

We investigate the impact of water on the optical absorption of prototypical silicon clusters. Our clusters contain 5 silicon atoms, tetrahedrally coordinated and passivated with either hydrogen or oxygen. We approach this complex problem by assessing the contributions of three factors: chemical reactivity, thermal equilibration, and dielectric screening. We find that the silanone (Si=O) functional group is not chemically stable in the presence of water and exclude this as a source of significant red shift in absorption in aqueous environments. We perform first principles molecular dynamics simulations of the solvation of a chemically stable, oxygenated silicon cluster with explicit water molecules at 300 K. We find a systematic 0.7 eV red shift in the absorption gap of this cluster, which we attribute to thermally induced fluctuations in the molecular structure. Surprisingly, we find no observable screening impact of the solvent, in contrast with consistent blue shifts observed for similarly sized organic molecules in polar solvents. The predicted red shift is expected to be significantly smaller for larger Si quantum dots produced experimentally, guaranteeing that their vacuum optical properties are preserved even in aqueous environments.